Electrical measuring apparatus



) Sept. 52 8, 1937.-

J. R. EATON ELECTRIC-AL MEASURING APPARATUS Filed Jan. 15, 1956INVENTOR.

JAME R- EATON mN N ATTORNEY.

" 2 an alternative arrangement e parallel combination ofresistor ill andcondenser 15 than sea. a 1931- v 2,094,207

' UNITED sr Tas I rar en- I 2,094,201 EILECTBIGALMEASURINGAPPABA'IUSJames a. Eaton, Jackson, Mich. Application January 15 1936,- Serial No.59,203 18 Claims. (cl. 175-183) This inventionrelates to improvements inelectransformer M, a grid M and, a plate 45; a mil trical measuringapparatus. ,liammeter 46 and a B battery 6]. Animportant object oftheinvention istoproe .The essential part of the measuring equipvide ameans for measuring the capacitance and ment consists of the highvoltage transformer equivalent resistance of devices, particularly lwhose secondary voltage is divided between electrical equipment such ascapacitors, insulathe test specimen M and the parallel combinatorsbushin gs, cable, etc. I tion of the resistor i1 and condenser it. By-'-A further'obje'ct'of the invention is; to provide vary g l1 d the d vo of h V l a means for measuring the-characteristics of the may beadjusted at. will. The transformer 6 in- 1 devices inIsitu. I W"sula'tes transformer if! from any. possible connec- Other objects ofthe invention will be apparent tion t5 groun through h pp y n t h duringthe course of the following description. result that all current P 8through Sp im n In the accompanying drawing: it has only one pathback'to the low voltage Fig. l'is a wiringdiagram'of the apparatus. endit of the secondary l2, namely through the .iust'abie capacitance andresistance in series. a 16; T Shield eliminates Stray p l ee In thedrawing, 4 is a connection to a suitable o Surrounding le r and'preventst w alternating current source which can .be concu e t to a und t ou-any path other than trolled by'switch 5..' insulating transformert o etest Specimen a dt veclnl'i llatien 20 5 has a primary land a'secondary8. The pr1-. of II and i8. "therefore, it is'apparent that the 20 mary Iis surrounded by a grounded shield 9. ent through M is the same as flowsthrou h From the'seco'ndary 8, connection is made to a the nt 1 B- Badiusting l1 step-up transformer I'll at its primary I l.- The n a thatno voltage exists b w p secondary 12.0! this transformer is connectedand ground th Veltfls 0! shield l8 will be from its high voltage end isto the ung'rounded zero a capacitance to nearby n d 25- terminal of thedevice It to be tested. The other lects will beeliminated. Moreoverunder conditerminal of the device is either permanently tion of zerovoltage on 22, the voltage between i6 temporarily connected to ground15:. The l and22 must be equal to and in phase with volt 'voltageend Itor the-secondary iris connected se between and As vcltace between I soto one'terminal of thevariableresistorl1 and and 22 must e in phas withvolta e between t 55 ll having'a cathode ,a' heata l2 supplied by a "co'nductors, an alternating voltage may appea 5Q one terminal pr thevariable condenser. l8, both a a d I vol e w n 16 d I5 m t e n of whichare in'turn connected to ground It. D c with Voltage between and Ualternate'arrangement -of the capacitance-rethese conditions thecapacitance and equivalent sistance combination l se -1e; lg'ghown mp1 2resistanceof the test specimen must be propor- 85A shield l9 surroundsthe secondary 8 01 the tethe capacitance and l'eeletanee 0! t '35transformer 8,-connecting to on nd 1 t combination of JLand la. Thecapacitance of ondary at It, the entire transformer in m the'specimenmay be calculated by dividing the fleeting-t0 its primaryat 2| d tgewndary capacitance of it by the ratio. of the voltage. tap 22, thehighvolta'ge connection-to the device between 22 and and the voltagebetween 40 to be tested u, and t n to the and322. The equivalentresistance of the speci- 40 sistor i'I-andcondenser ll. "is a 'iiwitch.v3 ment may b cal bvmui inlving the re- A voltage phaseshifting ani j uu. sistance'fof I! by this same ratio,

cuit consists of the midtap 2.4 of the transform The Presence Ragebetween a fi d .er' primary], a switch"; a transformer havis detected bythe indicating deviee mg a primary v a secondary a. an a the vacuumtube-voltmeter type. Closing switch 45:

1 twice to shah resistor so which is va'riabie from 9 alternating "maler h w zero" to infinity,.a reversing switch I] and a: afidahence went?0! this switch Wm a a c suit in a change in deflection of themillionpotentiometer 32, one end of which is grounded v 'at is u is thevariable ta "or the tentiommeter in me -m is being em t P I g:theo'f'the vacuum tube yolt- 50 v a e A voltage detecting deviceconsists of a con 2; 1g;- devlcef th ereb y tacit 13:15:;

denser 34, a switch 35, al'esistor 38,9. switch 81, v m n}; of "and" N Yi a condenser 38,-a 0 battery a thermionic tube when the .test set isoperated near energized 23 is opened and switches 5 and are closed,

thereby. leaving transformer l0 de-energi'zed while the voltage phaseshifting and adjusting device is energized. Condenser i8 is set at avalue esti- --mated to be approximately itssetting if used to' balancethe capacitance of the test specimen.

By varying the resistance between zero and infinity ohms, the voltageapplied to potentiometer 32 may be varied through 180 electricaldegrees. By use of the reversing switch 3| also, the voltage applied tothe potentiometer 32 may be of any desired phase position. Adjustment oftap .33 of the potentiometer 32 makes possible a selection of voltage ofany value within the limits of theequipment. This voltage phase shiftingand adjusting device, therefore, is able to apply to the cathode 4| analternating voltage of such phase position and magnitude that noalternating potential exists between 44 and 4 I as indicated by zerochange of deflection of the milliammeterwhen switch 35 is opened orclosed. Under such conditionswhen transformer I0 is energized by closingswitch 23, the alternating voltage between '44 and 4| will be dueentirely to the effects of voltage supplied by Hi. -The set may then beused in the usual manner with accurate results.

Operation of the equipment in the field is usually conducted as follows:With switch 5 open, switch 35 is opened and closed. If a change in thedeflection of the miiliammeter is noted, stray voltage is present on theset and must be balanced out by means of the phase shifting andadjusting device, If no change in deflection is noted, this a operationmay be omitted. To balance out stray voltage on the set, switch 23, isopened and switches 5 and 25 are closed. Resistance 30, re-

verslng switch 3i and potentiometer 32 are adjusted until no change indeflection is noted when switch 35 is closed andopened. Next, switch 23is closed applying test voltage to the specimen. If necessary, switch 31is closed to make the voltage indicating device less sensitive duringpreliminary adjustment, and then resistor l1 and condenser l3v areadjusted until no alternating voltage is indicated-between 3| and 4|.Switch 23- 'tance and equivalent resistance of electrical its equipmentunder alternating voltage stress comprising a source of alternatingvoltage having an intermediate tap, means for insulating this sourcefrom unwanted connections to ground, a combination of variableresistance and variable capacitance connected betweenone end of thevoltage 7 source and ground, a connection from the other end of thevoltage source to the ungrounded terminal of-the test specimen,the'other terminal of.

which is grounded, a shield which surrounds the voltage source, theconnections thereto, the con 7 I 2,094,907 between the grid 44 and thecathode 4! of the nection to the test specimen, and the connection tothe resistance-capacitance combination, a connection between theintermediate tap in the voltage source and the shield, a potentialdetecting device, and a device capable of producing a'voltage of anyphase position and of adjustable magnitude connected in series with thepotential detectingdevice between the intermediate tap of the voltagesource and ground.

2. Aninstrument for measuringthe capacitance and equivalent resistanceof electrical equipment under alternating voltage stress comprising asource of alternating voltage having an intermediate tap, means forinsulating this source from unwanted connections to ground, acombination of variable resistance and variable capacitance connectedbetween one end of the voltage source and ground, a connection from theother end of the voltage source to the ungrounded terminal of the testspecimen, the-other terminal of which-is grounded, a potential detectingdevice, and a device capable of producing a voltage of any phaseposition and of adjustable magnitude connected in series with thepotential detecting device between the intermediate tap of the voltagesource and ground.

3. An instrument for measuring the capacitance and equivalent resistanceof electrical equipment under alternating voltage stress comprising asource of alternat n'g voltage having an intermediate tap, means forinsulating this source fromunwanted connections to ground, a combinationof variable resistance and variable capacitance connected between oneend of the voltage end of the voltage source to the ungrounded terminalof the test specimen, the other terminal of which is grounded, a shieldwhich surrounds the voltage source, the connections thereto, theconnection to the'test specimen, and the connection to theresistance-capacitance combination, a connection between theintermediate tap in the voltage source and the shield, a potentialdetecting device connected between the intermediate tsp of the voltagesource and ground. v l

4. An instrument for measuring the capacivtance andequivalent resistanceof electrical equipment under alternating voltage stress comprising asource of alternating voltage having an intermediate tap, means forinsulating this source from unwanted connectionsto ground,-a combinationof variable resistance'and variable capacitance connected between oneend of the voltage source and ground, a connection from'the other end ofthe voltage source to the ungrounded terminal of the test specimen, theother terminal of which is grounded, a potential detectingde viceconnected between the intermediate tap of. the voltage source andground. A 4

5. An instrument for measuring the capacitive reactance and equivalentresistance of any .device under alternating voltage stress comprising, asource of alternating voltage, a combination of variable resistance andvariable capacitance connected in circuit with the voltage source andthe test specimem'means of comparing the magnitudes and phase relationof the voltage source and the voltage appearing across theresistance-capacitance combination. I

8; An instrument for measuring the capacitive reactance and equivalentresistance of any de vice under alternating'voltage'stress comprising,

a source of alternating voltage, a combination of resistance andcapacitance connected in circuit with the voltage'source and the testspecimen,

. 2,094,207 means'o! comparing the magnitudes and phase relation oi thevoltagesburce and the voltage appearing across theresistance-capacitance combination.

. and equivalent resistance oithe specimen, and an interferencebalancing means in operative rela- 7. An instrument for testingelectrical insulationunder alternating voltage stress comprising thecombination of circuits including a high 'alternating voltage circuit inwhich the specimen is arranged to be included and means by whichdeterminations may be made of the capacitance tion with said circuitsand provided with devices by which the effects of stray currents due tothe presence of nearby electrical conductors can be balanced out. i

8. An instrument for testing electrical insulation under alternatingvoltage stress comprising I the combinat on of circuits including a highvoltage circuit which the specimen is arranged to be included and meansby which determinations may be made of the capacitance and equivalentresistance of the specimen, interference balancing means in operativerelation with said circuits and provided with devices by which theeffects of stray currents due to the presence of nearby electricalconductors can be balanced out, and a shield for confining the eflectsoi the test voltage to the test specimen.

9. An instrument for testing electrical insulation under alternatingvoltage stress comprising. the combination of circuits including a highvoltage circuit in which the specimen .is arranged to tion underalternating voltage stress comprising the combination of circuitsincluding a high volt- 1 1 age circuit in which the specimen is arrangedto be included and anadjustable resistance and an adjustable capacitanceby which determinations may be made of thecap'acitance and equivalentresistance'oi' the specimen, and interference balancing'means inoperative relation with said cir.-

cuits and provided with devices by which the eflects of stray currentsdue to the presence of nearby electrical conductors can be balanced out.

l0. A'n'instrument for testing electrical insulabe included and anadjustable resistance and an adjustable capacitance by whichdeterminations may be made of the capacitance and equivalent resistanceoi. the specimen; interference bala'ncing' means in operative relationwith said circuits and provided with devices by which the eflects ofstray currentsndue to the presence of nearby electrical conductors canbe balanced out and a shield for confining the effects oi thetestvoltage.

to the test specimen. v a 1 11. An instrument for testing electricalinsulation under alternating voltage stress comprising the combinationof circuits including a high-voltage circuit in which the specimen isarranged to be included and means by which determinations may be'made oithe capacitance and equivalent resistance 0! the specimem andinterference bal- -ancing means inoperative relation with said citcultsand provided with devices by which the eflects oi stray currents due tothe presence of nearby electrical conductors can be balanced outincluding a' phase adjuster, a potentiometer and a voltmeter. v 12;. Aninstrument for testing electrical insulation under alternatingvoltagestress comprising the combination of circuits including a highvoltage circuitin which the specimen is arranged to ""bedncluded'and,adjustable resistance and an adjifitablecapacitance by whichdeterminations may be made the capacitance and resistance 'oi'thespecimen, and interference bal ancing means in operative relationwith said circuits and provided with devices by which the eflects ofstray currents due to the presence of nearby electrical conductorscan bebalanced out including a phase adjuster, a potentiometer and 'avoltmeter, the said adjustable resistance and cults and provided withdevices by which the efiects of stray currents dueto the presence ofnearby electrical conductors can be balanced out including a phaseadjuster, a potentiometer, a

voltmeter and a currentreversing switch.

l4. An instrument for testing electrical insulation under alternatingvoltage stress-comprising the combination of circuits including a highvoltage circuit in which the specimen is arranged to be included and anadjustable resistance and an adjustable capacitance bywhich"defterminations may be made of the capacitance and equivalentresistance of the specimen, interference balancmg means in operativerelation with said circuits and provided with de'vicesby; which theeflfectsof stray currents due to the presence of nearby elec tricalconductors can be balanced out including a phase adjuster, apotentiometer and a volt-- meter and by which voltmeter the adjustableresistance and the adjustable capacitance may be i adjusted to indicatezero'potential on the voltmeter and from whichtdjustments thecalculation of the energy loss may be determined, and shielding meansfor conflning'the eiiects oi the test voltage to the testspecimenr 1 15.An instrument iortesting electrical insulation under alternating voltagestress comprising the combination of circuits including a. high;

voltage circuit in which the specimen is arranged to be included, meansby which determinations may be made of the capacitance andequivalentresistance oi the specimen, interference balancing means in operativerelation with said circuits 1 and provided with devices by which theeffects of stray currents due to the presence of nearby electricalconductors can be balanced out including a. phase adjuster, apotentiometer and a voltmeter," said voltmeter being also used inconnection with the first mentioned means for securing saiddeterminations; a 1 v 16. An instrument for measuring the capacitanceand equivalent resistance -oi electrical equipment under alternatingvoltage stress comllrlsing a test transformer, the high voltage end ofwhich is'arranged to be connected to one side of a grounded specimen tobe tested, means for completing the circuihth 'ouzh-the specimen and theground tothe' low voltage end of the secondary of thetransiormer, anadjustable resist- .ance and capacitance in said last circuit between *0former. a. voltmeter connected into the primary a 7 the ground, and thesecondary ot-the test transcircuit oi-the transformer i'or indicatingwhen the voltage across the capacitance and resistance is in phase withthe test voltagev applied to the" s specimen, whereby the capacitanceand euuivalent resistance'ot the specimen can be determined directlyfrom the adjusted'indicated values of the resistance and capacitancerequired for balancing the circuit.

17. An instrument for measuring the capacitance and equivalentresistance of electrical equipment under alternating voltage stresscomprising a test transformer, the high voltage end of which is arrangedto be connected to one side of a grounded specimen to be tested, meansfor completing the circuit through the specimen and the ground to thelow voltage/end of the secondary oi the transformer, an adjustableresistance and capacitance in said last circuit between the ground andthe secondary of the test transformer, a voltmeter connected into'theprimary circuit of the transformer for indicating when the voltageacross the capacitance and resistance is' in phase with the test voltageapplied to the specimen, whereby the capacitance and equivalentresistance of the specimen can be determined directly from the adjustedindicated values of the resistance and capacitance required forbalancing the circuit, the adjustment of said re sistance andcapacitance to balance the circuit to the point at which no voltage isindicated on the voltmeter being effective to reduce the trans- .formerand all other connections except the circuit leading to the resistanceand capacitance and the connection to the specimen to substantially aground potential to negative the effect of stray capacitance.

18. The method of measuring the dielectric loss in insulating unitsadapted for high voltage alternating currents, which comprises applyinga test voltage to a grounded insulated specimen, causing the currentflowing, through the specimen to flow from the ground terminal throughanadjustable capacitance and adjustable resistance,-

